1. Field
The embodiments discussed herein relate to a superconducting current limiter device of the resistive type, the conductive track of which is formed by at least one band-shaped superconductor, a holding element being arranged between neighboring coil turns.
2. Description of the Related Art
In order to protect electrical components, a current limiter device may be constructed by using a superconductor. A characteristic of superconductors is the property that, below a material-specific critical temperature, they can carry currents virtually without resistance so long as the current density is less than a critical current density which depends on the operating temperature. This critical current density decreases with an increasing operating temperature, and it becomes zero when the operating temperature reaches said critical temperature.
This phenomenon can be utilized in order to construct a current limiter device which, in the event that the aforementioned critical current density is exceeded, abruptly increases its electrical resistance and is heated to above the critical temperature by the ohmic losses which then occur.
In order to avoid destruction by overheating, the current must be switched off after the current limiter has been tripped. In order to resume operation, it is necessary to wait until the entire limiter has cooled again to the operating temperature. This recooling time has an essential influence on the availability of the current limiter.
By utilizing this phenomenon, it is possible to construct a circuit breaker (current limiter) which is distinguished by rapid switching times and a switching process that is nondestructive for the protective device per se. Corresponding current limiter devices are known, for example, from DE 10 2004 048 646 A1.
As a conductor track in such a current limiter, superconducting band conductors (coated conductors) are used in particular. A superconducting band conductor in this context is intended to mean a structure in which a superconducting layer, typically an oxidic high-temperature superconductor, is applied onto a normally conducting substrate metal in band form. In order to avoid inductances, the superconducting band conductor is introduced into a flat, double-wound coil. A minimum spacing needs to be maintained between neighboring coil turns, so that a refrigerant can flow through the coil. If a high-temperature superconductor (for example YBCO) is used for the superconducting band conductor, then liquid nitrogen is suitable as a refrigerant for the current limiter device.
In double-wound coils made of band conductor material, the entire voltage drop across the coil is then applied in the region of the outer radius between neighboring conductor tracks. In order to allow a maximally compact design of the superconducting current limiter device, it is desirable to accommodate neighboring conductor turns in as small a space as possible. Consequently, the best possible insulation between neighboring turns is required in order to protect from electrical sparkover. At the same time, the availability of the superconducting current limiter device is crucially influenced by the recooling time of the superconductor after the switching process. Good accessibility of the refrigerant to the conductor track of the current limiter is consequently desirable. A superconducting current limiter device should furthermore be distinguished by the lowest possible inductance. To this end, it is advantageous that neighboring turns in the axial direction of the coil should ideally lie on a common plane surface, if possible. To this end, exact positioning of the turns of the superconducting current limiter is desirable.